1. How are these animals and plants linked?
Hint: What do you know about ecosystems?

2. Draw a desert food chain in your book.

3. Objectives
All students must be able to draw a simple desert food chain.
Most students should be able to give an example of a real desert plant and explain two adaptations
Some students should be able to explain desert food chains and webs in detail.

4. STRIPE:
Reflective learner - Present your learning in different ways when sharing your work with different groups of people

5. Syllabus key ideas: 5.1 Ecosystems in hot deserts are finely balanced.
5.2 Plants have adapted to survive in hot deserts.

6. What is the difference between a food chain and a food web?
A food chain only follows just one path as animals find food. eg: A hawk eats a snake, which has eaten a frog, which has eaten a grasshopper, which has eaten grass.
A food web shows the many different paths plants and animals are connected. eg: A hawk might also eat a mouse, a squirrel, a frog or some other animal. The snake may eat a beetle, a caterpillar, or some other animal. And so on for all the other animals in the food chain.
A food web is several food chains connected together.

7. Task 1
Your teacher will give you some cards with different desert plants and animals on them and some string.
Use these to create a food web similar to the one on the next slide.
What would happen to this web if one of the plants or animals in it disappeared?

8. A desert food web

9. So how do plants survive in the harsh desert environment?
How does this cactus cope with the lack of water in the desert?
How does it cope with the high evaporation rates?
How does it cope with the high temperatures in the desert?
How does this cactus protect itself from animals that want to eat it?

10. Note these key terms in your book:
Xerophytes – plants that have adapted to survive in very dry conditions
Dormant – when plants stop growing, for example in a drought
Ephemerals – plants that grow, flower and produce seeds within just a few weeks (following rain)

11. Barrel cactus
The shallow roots spread out around the plant to absorb moisture from rain or dew
The stomata (pores) are opened at night to exchange gasses for photosynthesis
This reduces the water lost out of the stomata
Inside the cactus is a mass of water-storing tissue
The cactus is covered with a thick waxy layer to prevent water loss and protect the plant from burning in the sun

12. Cistanche This plant is leafless, so can’t photosynthesise
It gets its ‘food’ by tapping the roots of other plants
This means that it is a parasite

13. Living stones These plants are camouflaged, so animals don’t eat them
They are succulents – they store water in their leaves
They grow with all but the tips of their leaves in the ground
The surrounding soil and stones protect them from the sun
They grow in southern Africa

14. Fire thorn branch Grows in deserts of SW USA
Sheds its leaves to conserve moisture in dry times
After rains new leaves grow among the spines
If the ground is wet enough it flowers

15. Welwitschia This plant has only two frayed strap like leaves
It has a huge tap root which may be 1m wide at the top
It grows on gravel plains in the Namib desert
It may live for a thousand years or more

16. Haworthia Grow in places with some shade
Only the tips of the leaves poke above the surface
In droughts the plant shrinks into the ground

17. Date palm Long roots to reach water Grown at an oasis
Small leaves reduce water loss
Dates are nutritious and don’t rot

18. Task 2
Choose one of the plants you have just seen and collect a photograph of it from your teacher
Draw the plant, filling a page, in your exercise book
Annotate (label) the plant to explain how it is adapted to the desert environment

19. Example:
The cactus has spikes instead of leaves, so it doesn’t lose as much water from evaporation.
The giant saguaro can store tonnes of water in its stems
The waxy skin protects from evaporation and sun burn

20. Reflection
Are some of you willing to present your sketches to the rest of the class, explaining how it has adapted to the desert environment.
Class vote for most informative sketches – award merits
When might annotated sketches be useful in an exam?

21. Have we achieved our objectives?
All students must be able to draw a simple desert food chain.
Most students should be able to give an example of a real desert plant and explain two adaptations
Some students should be able to explain desert food chains and webs in detail.